Cylinder Head - Revised Bolts and Torque Specifications

91mercedes01

REF. NO. 01/22


TO: OUR MERCEDES-BENZ PASSENGER CAR DEALERS

DATE: February 1991


SUBJECT: A. Engines 602.96, 603.96, 603.97 Cylinder Head Bolts with Increased Breaking Strength
B. Engines 601, 602, 603 Modified Tightening Specifications for Cylinder Head bolts


A. Engines 602.96, 603.96, 603.97 Cylinder Head Bolts with Increased Breaking Strength

In order to increase the tightening torque pre-load on the cylinder head bolts, modified cylinder head bolts with increased breaking strength are installed in production as of the engine end numbers listed in the table below.


Effective Serial Number

Model Engine As of Engine End Number

124.128 602.962 005247

126.134 603.970 000260
126.135


When performing a R&R of the cylinder head on any 602.96, 603.96, 603.97 turbodiesel engine, the previous version cylinder head bolts must be replaced with the modified version. The modified bolts may not be used on naturally aspirated diesel engines.

Figure 1:

The modified cylinder head bolt has a larger bolt head seat and increased breaking strength.

Identification

The modified bolt can be recognized by its code number and tabs on the bolt head.

Previous Version (A, Figure 1 )
Bolt head diameter 20.7 +/- 0.3 mm
Code number 85 or 850

Modified version (B, Figure 1)
Bolt head diameter 21.2 +/- 0.3 mm
Code number 95 or 950

Figure 2:

Two tabs on bolt head (arrows, Figure 2).


Parts Information

Part Name Part Number Length (mm)

Cylinder head bolts 603 990 01 10 80

603 990 02 10 102
603 990 03 10 115


B. Engines 601, 602, 603 Modified Tightening Specifications for Cylinder Head Bolts

A modified tightening specification for the cylinder head bolt (M10) is valid for the above mentioned engines, effective immediately.

The modified tightening specification allows the use of maximum bolt force to set the cylinder head gasket.

Note:
As always, it is extremely important to observe the cylinder head bolt tightening sequence (see microfiche job no. 01-145).


Tightening specification

1st Step 2nd Step 3rd Step Setting Time 4th Step

15 N-m 35 N-m 90~ 10 minutes 90~


M8 cylinder head bolts are still to be tightened to 25 N-m.